I see no strategy.
I see no sense in the change.
1.) The change has nothing to do with legally protecting the org. Otherwise, they would stop pioneers from reporting as well.
2.) Since restarting of public preaching activities after COVID-19, the biggest challenge for congregations has been to bring publishers to do door to door witnessing again. That's what CO's meetings with elders and MSs have been about all over the world in the last six months. And it were the detailed reports that identified that massive challenge for the org: Who has not been actively out for service in territory, but simply continued to craft some witness cards at home as done during pandemics? The lot of publishers who have been monthly reporting some hours without anymore reporting any placements/any return visits at all. So to stop detailed reporting foils PIMI elders' efforts to encourage those publishers to restart door to door witnessing.
3.) Even among elders and ministerial servants, there are quite a lot who have not yet restarted door to door service to the same extent they had done before COVID-19. So I personally was expecting that some elders and ministerial servants would have been deleted within next one or two years due to their lack of seal in field service. To stop detailed reporting makes it unnecessary or even impossible to delete such elders. But, of course, on a long run, this can't be a positive development for JWs' preaching activities.
4.) When org paused pioneers' hours goal during COVID-19 pandemic, many pioneers reduced their amount of time spent for preaching activities dramatically. This was a clear proof that lot of preaching work before had not been done due to unconditional love to Jehovah and to people in territory, but due to some social pressure in connection with hour goals and reporting. So the org knows well that to stop. detailed reporting will reduce hours spent in field service.
5.) First reactions in congregations to yesterday's announcement seem to be mixed. A lot of publishers appreciate this. But others start asking: why does the org create now an additional barrier between publishers and pioneers? Are publishers' hours worthless as only pioneers' hours have to be reported? Stopping detailed reporting would have been a chance to eliminate status-orientated way of thinking ("he is pioneer" vs. "he is just a publisher"). This opportunity has been missed; even worse, the gap between pioneers and rest of congregation will increase.